1. Field of the Invention
The present invention relates to an image forming apparatus having an optical scanner.
2. Description of the Related Art
Conventionally, there is an image forming apparatus that can correct a color shift in a sub-scanning direction on a photoconductor based on a timing at which a rotation reference position of the photoconductor is detected and an angular velocity of the photoconductor. Such an image forming apparatus is disclosed, for example, in Japanese Laid-Open Patent Application No. 2008-70802.
In such a conventional image forming apparatus, it is difficult to correct a sub-scanning misalignment of each of laser beams irradiated onto a photoconductor. The sub-scanning misalignment is generated due to a variation in a pitch (may be referred to as a beam pitch) of the laser beams in a sub-scanning direction caused by a difference in write-start timings of the laser beams. Thus, the conventional image forming apparatus has a problem in that a sub-scanning misalignment during an image forming operation cannot be corrected.